Shaded pole type motor for turntable drives



Nom 4, 194.4. E, v. SCHNEIDER 2,261,899

SHADED POLE TYPE MOTOR FOR TURNTABLE DRIVES Original Filed Sept. 14,1959 f n "11111111 A ,1/'amar .F Sa/wider Patented Nov. 4.,

UNITED STATES PATENT oFElcE zukl'g l suman ronrguriiglnclivrggz ron'rmmy Emmer V. Schneider', Ohio. signor to Oom Alliance,

Alliance Manufacturing Ohio, a corporation of Ohio Original applicationSeptember 14, 1939, Serial Divided and this application May 20, 1940,Serial No. 336,168 v (CL 17H78) l 1 Claim.

The invention relates to an induction motor drive for phonographturntables and the like, and contemplates certain improvements in theconstruction oi a shaded pole type of motor and the mounting therefor toproduce a simple, economical and eflicient friction drive for theturntable which will. operate quietly, at a uniform speed, andsubstantially free from mechanical or electrical vibrations, and thepresent application is a division of my co-pending application SerialNo. 294,938, filed September 14, 1939.

The recent revival of interest in radio phonograph combination units hascreated a considerable demand for a low priced, electric turntable drivefor phonographs. vThe essential requirements of a phonograph turntabledrive are quietness of operation, uniformity of speed, and freedom frommechanical and electrical vibrations.

Such turntables should rotate at a speed oi' '78.26 R. P. M. and thisspeed must be uniform, since any variation, in the speed results innoisy operation, producing what is commonly called wows or nutten A wowis caused by a variation in theV speed of each revolution of theturntable, and may be caused by gears that have a tight spot in everyrevolution of the shaft, or inthe case of a rim drive motor, it may becaused by irregularities in the turntable rim. Flutter issimilar to wowbut of a higher period of recurrence, and is generally caused bymechanical vibration, set up by unbalanced dynamic .forces in the rotorof the associated electric motor.

Other troubles encountered in phonomotor design are deviations in speedof the turntable, from the correct speed, due to variations in the linevoltage which operates` the motor, or variations in record drag causedby variations in sizes and cut of the records; changes in motor speeddue to temperature rise, or changes in turntable speed due to variousweight pickups.'

^ depending, peripheral turntable rim, whereby' the turntable isfrictionally driven from the motor.

Turntables for recording purposes, frictionally driven through themedium of an idler wheel, have been used for a number of years. However,in such machines relatively great weight of the parts and power surplusin the motor are relied upon to eliminate ,incorrect speed, wow,

nutten and 120 cycle hum in the recording style of friction idler wheeldrive; while the playback or reproduction unit, bceause of thelow costrequirement, must be designed to give the same quality of performancewithout surplus weight of A synchronous motor would naturally solve allf of the problems ot turntable speed variation, but such motors have thegreater fault of 120 cycle hum, and vibration in the '18.26 R. P. M.sub-synchronous type, and furthermore, are not selfstarting, for whichreasons they are not practical and have never come into extensive usefor this purpose. Synchronous motors of the selfstarting variety are tooexpensive to be used in such machines.

parts or surplus motor power.

Four pole motors running at 1600 to 1750 R. P. M. have always beenthought necessary both for gear drive and friction drive phonomotors,because the relatively slow speed rotor" generally does not make as muchnoise as rotor running at 3000 R. P. M.

The object oi the present invention is to provide a shaded pole motorand means of mounting the same for a phonograph turntable drive so as toovercome the objections and diiiiculties encountered in presentpractice.

Another object is to produce a turntable drive that is low in cost,quiet in operation and whichl will maintain the required uniform speedof rotation.

. A further object is to provide a two pole shaded type motor which willdrive the turntable quietly and at a more uniform speed, and'which canbe produced at a lower cost than the customary four pole motor generallyused at present.

A still further object is to provide a novel mounting for the motorwhich will eliminate noise and vibrations.

Another object is to provide a lcooling fanmounted upon the rotor shaftof the motor by means of a friction clutch to prevent injury to a personcoming into contact with the fan.

The above objects together with others which will be apparent from thedrawing and following description, or which may be later referred to,may be attained by constructing the improved motor turntable drive inthe manner illustrated in the accompanying drawing, in which Figure 1 isa vertical sectional view through a turntable drive equipped with theimproved motor; and

Fig. 2 is a bottom plan view of the motor and turntable drive.

Similar numerals refer to similar parts throughout the several views.

The turntable operating mechanism is mounted together as a unit upon abase plate I adapted to be seated upon and secured to the platform I Iof the cabinet or other support for the phonograph as indicatedgenerallyin Fig. i, occupying a position over the opening I2 in the platform.

The base plate I0 is provided with an opening I3 through which the motoris mounted as will be later described.

The motor supporting plate I4 is mounted spaced above the base plate I0and over the opening I3 thereof, by means of rubber grommets I5 andspacers I6, and a plurality of depending posts I are fixed to said motormounting plate and extend downwardly through the opening I3 in the baseplate for the purpose of supporting the motor which will be laterdescribed. l

A post I8 extends upwardly from the base plate, being preferablyjournaled therein in any suitable manner, and the hub I3 of a turntableof sheet metal or the like may be fitted thereover.

The post I8 provides a fixedmounting for the turntable as its axisremains stationary, and the turntable when positioned upon this post isadapted to revolve freely about the same.

The turntable is provided with a depending peripheral flange 2|; theinner face of which is adapted to engage the friction tread 22, prefer-.ably a hollow rubber tire filled with a suitable liquid such asglycerin, liquid soap or salt brine, fitted peripherally about an idlerwheel 23 which is mounted` to revolve about a stud 24 carried near theouter end of the plate 25.

This plate 25 may be mounted for sliding or swinging movement upon themotor mounting plate I4 in the manner disclosed in detail in myco-pending application, Serial No. 294,938 above referred to.

Since the present Y application pertains to the motor it is not thoughtnecessary that the detail construction and mounting of this plate befurther disclosed herein.

The motor which drives the turntable through the friction wheel 23 is atwo pole shaded pole type motcr, the stator or field member of which iscomposed of a stack of laminations 32 stamped from sheets of magneticiron and connected to the depending rods I'I whereby the motor issuspended from the motor mounting plate I4.

This motor is of a non-concentric design, the stator or field memberbeing substantially rectangular in shape with a central opening 33therein so that one end of the stator may be surrounded by a coil 34 ofwire secured upon an insulation spool 35, the ends of the coil beingconnected to the wires 35 which may lead to any suitable source of'electric energy.

At the opposite end of the motor the stator laminations are apertured toprovide a substantially circular opening 31 for receiving a cylindricrotor 38 of the squirrel-cage type. The laminations are cut away ondiametrically opposite sides of this cylindric opening forming air-gapsas indicated at 39, heavy iron sheets 40 being inserted between the endsof the opposite pole pieces 4I thus formed.

A single shading coil 42 surrounds each pole piece and the inner facesof the poles are cut away as at 43 on diametrically opposite sides sothe opposite sides of the stator and a small pulley frictionally engagesthe 41 is fixed upon the upper end of the shaft and periphery of thefriction wheel 23.

A cooling fan 48 may be mounted upon the lower end of the shaft 4l bymeans of a friction clutch formed of a felt washer 43 and ber washers 50so that the fan will be instantly stopped without injuring a personshand which may come in contact with the same.

The turntable drive unit above described has many advantages over theumts now in general use, one advantage of considerable importance beingthe low cost of the two pole motor as compared to a four poled motor.

Another advantage resulting from the use of a two pole motor is that thehigher speed rotor allows a greater reduction either by gear or idlerwheel than the four pole motor. Thus, the turntable and record speed areless affected by changes in rotor speed of a 3000 R. P. M. two polemotor than in a 1600 or 1700 R.. P. M. four pole motor.

The higher speed rotor and greater reduction also gives greater freedomfrom wows because of the inertia of the high speed rotor working throughthe higher ratio of reduction.

By the use of a small diameter rotor the higher rotor speeds encounteredcause no additional vibration due to dynamic unbalance, magnetic pull,etc. over that of the conventional four pole motor.

Furthermore, the unique method of mounting the motor minimizes thetransfer of existing motor vibration to the record and on through thepick-up to be amplified and cause disturbance in the audiblereproduction.

By mounting the base plate carrying the stud on which the turntablerevolves in the manner illustrated and described solidly to the cabinet,this construction provides high inertia due to the mass and weight ofthe entire cabinet to any vibration, thus maintaining the turntable freeof motor vibration.

The idler wheel 22 is free to rotate in the bearing carried by the plate25, this plate being free to slide over the surface of the motormounting plate in such manner as to retain proper vertical position,while free to slide horizontally, this construction being so designed asto minimize wedging tendencies under varying load conditions.`

It is well-known to those skilled in the art that such wedging action asencountered where the points of contact of the motor drive pulley andthe turntable rim are approximately diametrically opposite each othercreates an unstable turntable speed condition which is the cause ofobjectionable wows" or transient fre-A quency variations in reproductiondue to uneven turntable speed.

In the present invention a relation of more nearly ninety degreesbetween the motor drive pulley and turntable point of contact on theidler wheel is maintained in order' to minimize this wedging action andatvthe same time provide a positive drive to the depending rim flangeoi!l the turntable.

I claim:

A phonograph turntable drive including a two pole shaded pole type motorcomprising an elongated stator, a squirrel-cage rotor rotatably mountedwithin one end of the stator, the stator being divided into salientpoles, diametrically opposite shading coils on said salient'poles, saidshading coils dividing each salient pole into a shaded pole portion andan unshaded pole portion, each shaded pole portion being approxi-kmately one-half the pole iace circumference of

